First-Principles Investigation on Electronic Properties of Quantum Dot-Sensitized Solar Cells Based on Anatase TiO2 Nanotubes

The first-principles quantum mechanical investigation on CdS quantum dots (QDs) adsorbed on anatase TiO2 nanotubes (TiO2NTs) in quantum dot-sensitized solar cells (QDSSCs) was performed using the density functional theory (DFT) approach. The geometry and electronic coupling between a CdS QD and the TiO2NT have been examined for the first time, together with a detailed discussion of interfacial electron transfer and electron transport models along the TiO2NT. It has been found that adsorbate states are introduced in the band gap of the TiO2NT upon the adsorption of a CdS QD on the TiO2NT surface, and an electron transfers from the sulfur atoms of a CdS QD to the conduction band of the TiO2NT upon adsorption of visible light. The unique TiO2NT structure offers a one-dimensional directional pathway for electron transport across the semiconductor substrate through titanium d(x2-y2) and d(z2) orbitals. Our work is of great benefit for understanding the charge separation process at the heterogeneous interface and the key factors to govern the electron transport efficiency in TiO2NTs.